Auditory Prostheses & Perception Lab

Overview

The APPL conducts research on various aspects of hearing with cochlear implants (CIs). Along the way, we are also learning a great deal about how the normal brain processes degraded sounds/speech. Specific current projects include i) studies of pitch/intonation/lexical tone perception by children and adults with CIs, as well as their normally hearing peers; ii) examining aspects of the auditory nerve response to electrical stimulation as reflected in perceptual measures; iii) how the CI listener processes multi-channel, complex electrical stimuli. Collaborations with Dr. Rochelle Newman at the University of Maryland and Dr. Deniz Baskent at the University of Groningen investigate various aspects of the perception of degraded speech by infants, toddlers and adults. In addition, in new collaborations with Dr. Yung-Song Lin at Chi-Mei Medical Center in Tainan, Taiwan, and Dr. Charles Limb at Johns Hopkins University, Baltimore, MD, we are investigating the processing of voice-pitch information by early-implanted children who are native speakers of Chinese (Taiwan) and American English (US).

Facilities

The APPL area includes one large sound booth for conducting listening tests in quiet environments, an adjacent room from which sounds delivered to the booth are controlled and experiments monitored, and an outside area in which experiments involving direct electrical stimulation of the implanted device are conducted.

Summary of Research Program

For Scientists/Clinicians

The long-term objective of our lab is to understand basic mechanisms underlying auditory processing by cochlear implant listeners. Our experiments include psychophysical measures of listeners’ sensitivity to single and multi-channel, steady-state and fluctuating electrical stimuli, measures of speech intonation and lexical tone recognition, and the recognition of degraded speech by both normally hearing and cochlear implanted individuals. New research centeres on i) effects of auditory-nerve degeneration on the coding of spectro-temporal aspects of the signal, and ii) potential beneficial effects of early implantation on auditory perception through the device.

For Cochlear Implant Patients and Normally Hearing Participants

Our lab conducts studies on cochlear implant patients’ perception of sounds – ranging from simple to complex sounds, and, of course, speech perception. In typical experiments, we ask participants to detect subtle differences between sounds (differences in pitch, loudness, timbre, etc.). Alternatively, listeners may be asked to identify vowels or consonants (for instance, did you hear apa or aba or aja? Hit or heat?), or recognize the intonation pattern in a speech sound (did it sound like a question or a statement?), or to simply repeat back a sentence they heard. Parallel studies with normally hearing listeners investigate how the brain processes sounds that have been altered to simulate cochlear implant processing. The ultimate goal is to contribute to improved devices, processors, and training/rehab of patients in the future by improving our understanding of the basic mechanisms involved in cochlear implant hearing.

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